This command…
for i in * ; do j=`echo $i | sed ‘s#Matt#Cyberfella#g’ – ` ; mv “$i” “$j” ; done
turns a file listing like this…
Matt_001_blah.txt
Matt_002_blah-de-blah.txt
Matt_003_blah.txt
into this…
Cyberfella_001_blah.txt
Cyberfella_002_blah-de-blah.txt
Cyberfella_003_blah.txt
Just change the search and replace strings accordingly to swap a common text string occurring in the filenames to something else (or leave the replace string blank to eradicate it).